1. Field of the Invention
This invention relates to a vinyl copolymer having a silanol group in a side chain, more particularly, to a silanol group-containing vinyl copolymer which offers a room temperature curable resin composition of one pack type which crosslinks in the presence of moisture into a cured coating having weatherability, flexibility, and adherence and is thus suitable as a coating agent. It also relates to a method for preparing the copolymer and a room temperature curable resin composition containing the copolymer.
2. Prior Art
In the prior art, acrylic urethane resins, acrylic silicone resins, and fluorinated resins are known as useful resins for paint, especially useful resins for use in room temperature curable coating compositions having weatherability. Among these resins, acrylic urethane resins are less expensive, but use as the source reactant isocyanates which are harmful to the human body. Fluorinated resins have weatherability, but are expensive. In contrast, acrylic silicone resins are recently under increasing demand because of a good compromise between performance and cost.
The acrylic silicone resins have an alkoxysilyl group attached to an acrylic backbone. The acrylic silicone resins can form stable cured coatings when applied to supports because alkoxysilyl groups react with moisture in air at room temperature to produce siloxane bonds. See Coating and Paint, No. 429, pages 55-64. An alkoxysilyl group can be introduced into an acrylic backbone, for example, by copolymerizing a polymerizable vinyl group-containing silane compound in the presence of a radical initiator as disclosed in Japanese Patent Application Kokai (JP-A) No. 36109/1982.
However, the conventional acrylic silicone resins fail to impart weatherability as high as fluorinated resins and enough flexibility to meet a wide variety of applications. There is a need for an acrylic silicone resin having these properties.
Most methods of preparing acrylic silicone resins are of solution type using organic solvents and most of acrylic silicone resin compositions are also of solution type, both failing to meet the current trend toward non-pollution and resource saving. Known methods for carrying out copolymerization in aqueous media without using organic solvents include emulsion polymerization and suspension polymerization. With these methods, however, hydrolyzable groups to be retained, such as alkoxysilyl groups, react with water to crosslink during copolymerization or storage, inducing inconvenient thickening and gelation.